Battery Circuit

tappan · Post by **tappan** » Fri Jan 28, 2005 9:26 am

I'm working on a n64p. It's going to have two 8.4V 3000mah NiMh batteries.
Each is composed of 7 subC batteries. I'm going to be running them parallel so that I can get 6Ah. My trouble is, is that I also want to be able to supply power from a dc adaptor. And maybe have it trickle charge the battery. I also do not want to have to remove the batteries from the case every time I need to charge them.

I would like the circuit to:
1) Switch from battery power to external power when it external power is supplied.
2) Be able to either/or:
a) charge the battery while the portable is running off an external power source. (trickle)
b) charge the battery when the portable is turned off. (straight charge)
3) Be a fairly simple circuit( lol, I'm a newb. ).

Or, if you can't supply me with a diagram, maybe you could just give me info on calculating the voltage/amperage needed to charge my two batteries at once.

thanks for your time,
Jon

Post by **gannon** » Fri Jan 28, 2005 9:50 am

I'm not sure how to trickle charge NiMH batteries, but it probably only requires the use of a current limiting resistor.
As for the other stuff, get a switching DC jack that automatically switches, and then put a switch in that provides power to the charging circuit.

tappan · Post by **tappan** » Sun Jan 30, 2005 10:28 am

Okedoke... I got a DC jack with a switch. Can you explain to me, though, how I'm supposed to wire it?

Here's a redraw of the diagram on the back of the packaging:

http://img.photobucket.com/albums/v629/ ... dcjack.gif
(4k)

Any help is greatly appreciated.

Post by **Gamelver** » Sun Jan 30, 2005 12:50 pm

well, first you'd attach a wire to the postive input pin. then, attach the wire from the batteries to the pin that connects to the switch part (the part that gets shut off when you plug in the external power source). finally, simply attach the negative input pin to ground and it should work fine

.

A.J. Franzman · Post by **A.J. Franzman** » Sun Jan 30, 2005 1:45 pm

That will take care of disconnecting the batteries when running from external power.

You'll still need to connect your charging circuit, which could be as simple as a resistor across the switched and shell (ground) terminals.

tappan · Post by **tappan** » Sun Jan 30, 2005 1:46 pm

Could you relate that to the diagram?
i.e. Center pin connector being external negative.

Would I attach the Shell to ground, and the battery's negative to the other connector?
i.e.

http://img.photobucket.com/albums/v629/ ... cjack2.gif
(5k)

And as to the 'charging' circuit, would I need to run it at 8.4v?
I know that I would need to limit the amperage, but would I need to input exactly 8.4v?

A.J. Franzman · Post by **A.J. Franzman** » Sun Jan 30, 2005 2:16 pm

Do you already have a wall wart that is negative ouput at the tip/center? Because you've drawn it with non-standard polarity (although there are some devices like this, they're not as common).

Normally the tip or center of the plug is positive. Assuming yours is also:

The center terminal would go to the circuit (+) and battery (+).

The shell terminal would go only to the circuit (-).

The switched terminal would go to battery (-), as you indicated. Be sure this terminal does not connect to anything when a plug is in.

If you can live with just a trickle charge, put an appropriately sized resistor between the shell terminal and switched terminal.

If you're not sure about polarity, put a diode between the jack center terminal and circuit board/battery. The stripe on the diode will need to be on the end away from the jack.

tappan · Post by **tappan** » Sun Jan 30, 2005 3:52 pm

Thanks A.J.
That was exactly what I was looking for.
And yes... I was quoting the polarity wrong.

But as for my second question...
Does the input voltage for the trickle charger need to be the same voltage as the battery?

A.J. Franzman · Post by **A.J. Franzman** » Sun Jan 30, 2005 9:57 pm

The input voltage will need to be higher than the battery voltage, and you will need to find out how much current the trickle charge should be. Then calculate the needed resistance using the difference between the fully charged battery voltage and the supply voltage.